We have investigated the pretreatment effects on the lengths and the diameters of carbon
nanotubes (CNTs) grown on a Ni catalyst by using dc plasma-enhanced chemical-vapor deposition system.
The average sizes of the Ni particles changed with the cathode bias during the pretreatment, with the
minimum value at a cathode voltage -100 V. The diameters of the CNTs followed the size of the Ni
particles. In the cathode voltage range from -100 V to -600 V, the average diameter of the CNTs changed
from 31.7 nm to 66.5 nm with increasing Ni sizes. The plasma power and the pretreatment time should be
optimized to control the diameters of vertically-aligned CNTs. Also, N 2 is added in NH3 during the
pretreatment, the lengths and the densities of the CNTs can be controlled.
